1. Field of the Invention
The present invention relates to an apparatus for supporting an optical system including an objective lens for projecting a light spot onto an optical information record medium in an optical information recording and/or reproducing apparatus. The present invention also relates to a method of proving a damping member in the apparatus for supporting the optical system.
2. Related Art Statements
In an optical information recording and/or reproducing apparatus, a light beam is projected onto an optical information record medium by means of an optical system having an objective lens opposing to the optical information record medium. In this case, the objective lens has to be supported movably in a direction parallel to an optical axis of the objective lens as well as in a direction perpendicular to the optical axis of the objective lens. In the specification, the direction parallel with the optical axis of the objective lens is called a focusing direction, because by moving the objective lens in this direction, it is possible to perform a focusing control for focusing the light beam on an information track on the optical record medium. A direction perpendicular to the optical axis of the objective lens as well as to a track direction in which the information track extends is called a tracking direction. By moving the objective lens in the tracking direction, the light spot can be moved in a radial direction of a disk shaped optical information record medium to perform a tracking control. A direction perpendicular to the focusing direction as well as to the tracking direction is termed as a tangential direction. By moving the objective lens in the tangential direction, a so-called time base error can be corrected. By moving the objective lens in the focusing direction as well as in the tracking direction, the light spot can be precisely controlled to follow the information track although the optical information record disk is rotated eccentrically in an inclined plane.
In order to perform the focusing and tracking control, the objective lens is supported movably at least in the focusing direction and tracking direction by means of a plurality of resilient supporting members such as wires and leaf springs and is moved in the focusing direction and tracking direction by energizing an electromagnetic accutuator in accordance with focusing error signal and tracking error signal. In this manner, the objective lens is supported by a two-dimensional driving mechanism, In order to operate the two-dimensional driving mechanism stably, it is necessary to suppress a primary resonance of the supporting members effectively. Further, it is preferable to suppress higher order resonances of the supporting members.
In Japanese Patent Laid-open Publication Kokai Sho 56-94311, there are proposed various objective lens supporting apparatuses, in which damping can be attained. As shown in FIG. 1, an objective lens 200 is held by a holding member 201 which is supported by one ends of two leaf springs 202 and 203, whose other ends are secured to a stationary member 204. To the holding member 201 are secured permanent magnets 205 and 206 at opposite surfaces of the holding member. Magnetic circuits are formed by the permanent magnets 205 and 206 together with yokes 207, 20B, 209 and 210 and permanent magnets 211 and 212. Within gaps between the yokes 207 and 208 and the magnets 205 and 206, there are provided magnetic fluids 213 and 214, respectively.
In case of filling a gap between a movable member and a stationary member with a liquid damping material, it is rather difficult to maintain the liquid damping material within the gap and the damping material is liable to spread particularly when a moving range of the movable member is large. In the known optical system supporting apparatus illustrated in FIG. 1, the magnetic fluid is used as a liquid damping material, so that the damping material can be retained within the gap by a magnetic force. In this case, the damping material is limited to the magnetic fluid and non magnetic damping member having various damping properties could not be used. Moreover a portion which is filled with the magnetic fluid is limited to the magnetic circuit, and an amount of the damping material with which the gap is filled is also limited.
FIGS. 2A, 2B and 2C show another known optical system supporting apparatus described in Japanese Patent Application Laid-open Publication Kokai Sho 61-258346. A holding member holding an objective lens 215 of an optical system is secured to one ends of two focusing leaf springs 216a and 216b whose other ends are secured to a connecting member 217a. The connecting member 217a is coupled with a stationary member 118 by means of a tracking leaf spring 217b. Above a portion of the focusing leaf springs 216a and under a portion of the focusing leaf spring 216b near the connecting member 217a there are arranged cover plates 219a and 219b, respectively, said portions of the leaf springs 216a and 216b and the cover plates 219 are embedded within damping members 220a and 22b, respectively made of a viscous material. As can be clearly shown in FIG. 2C, a portion of the tracking leaf spring 217b near the connecting member 217a is also embedded in a damping member 220c. There is further provided an intermediate member 221 between the focusing leaf springs 216a and 216b. The intermediate member 221 functions to deform the damping members 220a and 220b efficiently so that a damping effect improved.
In this known apparatus, since the focusing leaf springs 216a, 216b are surrounded by the cover members 219a, 219b and intermediate member 221 and spaces formed therebetween are filled with the damping members 220a, 220b, the spread of the damping members can be prevented. However, the number of parts is increased and the apparatus becomes complicated. Also, costs are increased accordingly.
In Japanese Patent Application Laid-open Publication Kokai Sho 58-182142, there is disclosed another known optical system supporting apparatus as shown in FIG. 3. In FIG. 3, an objective lens 230 is held by a lens holding member 231 and this lens holding member 231 is supported by means of two supporting members 236a and 236b movably in the tracking direction with respect to a stationary member 237, The supporting member 236a is formed by a composite leaf spring including a pair of leaf springs 232a and 232b and silicone resin layer 234a and viscous rubber layer 235a sandwiched between the leaf springs 232a and 232b. Similarly the supporting member 263b is also formed by a composite leaf spring consisting of a pair of leaf springs 233a and 233b and silicone resin layer 234b and viscous rubber layer 235b sandwiched between the leaf springs 233a and 233b. Such a supporting member 236a, 236b is called a constrained type damping member. The damping member of constrained type has a limited function and the primary resonance could not be suppressed effectively. Furthermore, a mutual relationship between these two leaf string members 236a and 236b.
FIG. 4 depicts another known supporting apparatus described in Japanese Patent Application Laid-open Publication Kokai Sho 59-124042. An objective lens 240 is secured to a lens holding member 241 and the lens holding member is supported by a pair of leaf springs 242a and 242b movably in the tracking direction. The leaf springs 242a and 242b are secured to a stationary member 243 which is shaped such that lengths of the leaf springs 242a and 242b are different from each other. In this manner, resonance frequencies of the leaf springs 242a and 242b differ from each other so that a peak of a resonance of a whole supporting apparatus is reduced.
In this known optical system supporting apparatus, there is not provided any means for defining a mutual relation between the two leaf springs 242a and 242b.
In Japanese Patent Application Laid-open Publication Kokai Hei 5-46999, there is described another known apparatus for supporting the optical system as illustrated in FIG. 5. An objective lens 245 is secured to a lens holding member 246 and this lens holding member is supported by four resilient wires 247a, 247b and 247c, 247d movably in the focusing direction as well as in the tracking direction with respect to a stationary member 248. Effective lengths of these wires 247a-247d are the same, but portions of the lens holding member 246 at which one ends of the wires 247a and 247b (not shown in FIG. 5) are shifted with respect portions of the lens holding member at which one ends of the wires 247c and 247d (not shown in FIG. 5) are secured, and similarly portions of the stationary member at which the other ends of the wires 247a and 247b are secured are shifted with respect to portions of the stationary member at which the other ends of the wires 247c and 247d are secured. Also in this known optical system supporting apparatus, a resonance frequency of the wires 247a, 247b is shifted with respect to a resonance frequency of the wires 247c, 247d so that a peak of a resonance of the whole supporting apparatus can be reduced, but there is not provided any means for damping the resonance.
In Japanese Patent Application Laid-open Publication Kokai Hei 2-232824, there is proposed another known optical system supporting apparatus. In this apparatus, as shown in FIGS. 6A and 6B, an objective lens 251 is held in a lens holding member 252 and the lens holding member is supported by four resilient wires 253 movably in the focusing direction as well as in the tracking direction. Substrates 256 are secured to the lens holding member 252 and one ends of the wires 253 are secured to the substrates 256 by solderings 257. A substrate 255 is secured to the stationary member 254 and the other ends of the wires 253 are secured to the substrate by solderings 257, In order to suppress the undesired first order resonance, in the lens holding member 252 there are formed recesses 252a around the wires 253 and these recesses are filled with damping materials 259. Similarly, recesses 254a are formed in the stationary member 254 around the wires 253 and are filled with damping materials 259. The damping members 259 are made of gel-type damping material.
In case of suppressing the undesired resonance of the supporting apparatus by using a fluidizable damping material such as gel- or sol-type damping materials, gelatine-type damping materials, silicone oil damping material, it is necessary to provide a means for holding the damping material in position otherwise the damping material might be spread or flowed. To this end, in the above mentioned known apparatus, the recesses 252a and 254a are formed and the fluidable damping materials 259 are injected into these, recesses as best shown in FIG. 6B. However, in this case, an amount of the damping material injected into the recess fluctuates as illustrated in FIGS. 7A and 7B. In FIG. 7A, an amount of the damping member 259 is too small so that a length L of a portion of the leaf spring 253 embedded in the damping member is shorter than a desired value. In FIG. 7B, an excessive amount of the damping material 259 is injected into the recess 254a and thus a length L of the leaf spring 243 surrounded by the damping material is longer than a desired value. In any case, a resonance frequency of the supporting apparatus is changed and a desired damping property could not be attained.
In Japanese Patent Application Laid-open Publication Kokai Hei 6-76331, there is described another known optical system supporting apparatus. As depicted in FIG. 8, an objective lens 261 is held by a lens holding member 262 and the lens holding member is supported by four leaf springs 263a-263d movably in the focusing direction as well as in the tracking direction with respect to a stationary member 264. Between the leaf springs 263a and 263b is provided a damping member 265a and between the leaf springs 263c and 263d is arranged a damping member 265b. In this known supporting apparatus, the damping members 265a, 265b are provided between a pair of leaf springs 263a, 263c and 263b, 263d, so that a good damping property is obtained.
The above mentioned publication also discloses an optical system supporting apparatus illustrated in FIG. 9. In this apparatus, lugs 266a-266d formed in the leaf springs 253a-253d, respectively, and a damping member 265a is provided between the lugs 266a and 266b and a damping member 265b is arranged between the lugs 266c and 266d.
In these known apparatuses, the damping members 265a and 265b are not made of the above mentioned fluidable damping material, but are constituted by previously formed damping blocks made of a resilient material. In case of using such a previously formed damping member, various portions have to be manufactured to have predetermined dimensions and shapes so that the damping member can be provided in position. Therefore, a cost of manufacturing the supporting apparatus is liable to be increased.
In Japanese Patent Application Laid-open Publication Kokai Hei 5-325219, there is shown another known optical system supporting apparatus. As shown in FIG. 10, a lens holding member 272 holding an objective lens 271 is supported by a pair of leaf springs 273a and 273b movably in the focusing direction as well as in the tracking direction with respect to a stationary member 274. The stationary member 274 includes a projection 275 extending between the leaf springs 273a and 273b, and parts of the leaf springs are embedded in damping members 276a and 276b made of a viscous material.
In this known optical system supporting apparatus, the damping members 276a and 276b made of a viscous damping material are used so that the damping material does not spread although a means for supporting the damping material is not provided. However, an amount of the damping material applied to the leaf spring 273a, 273b is liable to fluctuate so that a desired damping property could not obtained easily. Moreover, this structure-could not be applied to the apparatus using a fluidable damping material.